Explanation:
What is that strange material on Mercury?
When
flying by Mercury last October, the robotic
MESSENGER spacecraft imaged much of the solar system's
innermost planet
in unprecedented detail.
As common in science, new data bring new mysteries.
Pictured above on the lower right, a large crater -- about 100 kilometers across --
has unusual dark material of unknown composition near its center.
The material's darkness does not appear to be caused by
shadows, as the Sun was near
zenith
when the image was taken.
One origin hypothesis is that the
dark material was uncovered from
beneath Mercury's surface during the impact that created the surrounding crater.
If so, the composition of the dark mound might be similar to the composition of some
mysteriousdark rings
also recently discovered on Mercury.
Alternatively, the dark material could be related to an unusual composition of the impacting rock.
MESSENGER will
buzz past Mercury again later this year before entering orbit in 2011.